Patent Literature 1 discloses that an imidazole compound, one of the active ingredients in the agricultural or horticultural fungicide composition of the present invention, is useful as a harmful bio-organism controlling agent. In addition, it also discloses that if necessary, the imidazole compound can be mixed with or used in combination with other fungicides. Furthermore, Patent Literature 2 discloses polyoxins as antibiotics. However, these literatures do not disclose the combination of active-ingredient compounds in the agricultural or horticultural fungicide composition of the present invention.